PS-Pd–NHC: an efficient and heterogeneous recyclable catalyst for direct reductive amination of carbonyl compounds with primary/secondary amines in aqueous medium

Abstract

A highly efficient polymer supported palladium-N-heterocyclic carbene (PS-Pd-NHC) catalytic system has been developed for direct reductive amination (DRA) of carbonyl compounds with primary/secondary amines in aqueous reaction medium. This new catalytic system represents a heterogeneous, recyclable and environmentally benign protocol. The developed methodology describes a simple one step approach for the synthesis of a wide variety of substituted amines exhibiting remarkable activity with excellent yield of a desired product. Furthermore, the catalyst was effectively recycled for six consecutive cycles without any significant loss in its catalytic activity.

Transfer hydrogenative reductive amination of aldehydes in aqueous sodium formate solution

“…Addition of 0.5 equiv of HCO 2 H produced 40% of 5 and 19% of 6 (entry 2). Under these conditions, the selectivity toward the desired amine product over benzyl alcohol was inferior, however, delightful results were observed after adding additional HCO 2 H. The selectivity of 5 versus 6 was enhanced as more HCO 2 H was added, however, the tradeoff was that the conversion of benzaldehyde was reduced (entry [4][5][6][7][8][9][10][11]. This phenomenon indicates that the hydrogenation of benzaldehyde was significantly suppressed at lower pH, whereas the reverse reaction of imine formation was accelerated under the same conditions.…”

“…Afterward, several groups have developed different methods of aqueous reductive amination based on either hydride reagents or hydrogenation using gaseous H 2 . [6][7][8][9][10][11] However, these reactions usually suffer some drawbacks, such as the requirement of high temperatures and moderate to high pressures, or poor atom economy. Xiao and co-workers [12][13][14][15][16] have pioneered in the catalytic transfer hydrogenation reactions in water.…”

Solvent‐Switchable Regioselective Synthesis of Aurones and Flavones Using Palladium‐Supported Amine‐Functionalized Montmorillonite as a Heterogeneous Catalyst

“…We started our investigation with the aim to achieve a better yield and higher regioselectivity for the model reaction using Pd 0 APTES@K10 catalyst (0.05 g) and CO (60 psi) in 1,2‐dimethoxyethane (DME). For regioselective cyclization, Baldwin described the rules to predict the favorable modes of cyclization, that is, 5‐ exo or 6‐ endo . Initially, with the implementation of triethylamine (NEt 3 ) as a base, we obtained a good conversion with a combined yield of 3 a / 4 a in the ratio 75:25 %, whereas N , N ‐diisopropylethylamine (DIPEA) gave a better selectivity towards the formation of 3 a , but the combined yield was lower (Table , entries 1 and 2).…”

Recent Advances Utilized in the Recycling of Homogeneous Catalysis

“…By using this catalytic protocol excellent yields of the products were achieved at solvent‐free conditions (Scheme ) . Our group developed a polymer‐supported palladium‐ N ‐heterocyclic carbene complex (PS−Pd−NHC) by using Merrifield resin and utilized for various transformations such as selective conjugate reduction of unsaturated carbonyls in an aqueous medium and reductive amination of carbonyl compounds with amines . This polymer‐supported catalyst was easily separable by using a simple filtration method with a very negligible loss in its weight.…”